A product has a characteristic value, which indicates a predetermined characteristic, measured before shipment, and is discriminated to a non-defective article or a defective article depending on whether or not a predetermined standard is satisfied. The product is discriminated by comparing the measured characteristic value of the product and a inspection standard, of which condition is stricter than a product standard (a characteristic value required for the product), using a product inspection device. If the variation in the measured characteristic values of the products is only the variation in the characteristic values of the products themselves, whether each of the products is a non-defective article or a defective article can be correctly discriminated by the product inspection device even if the inspection standard is defined under the same condition as that of the product standard.
However, the variation in the measured characteristic values of the products includes not only the variation in the characteristic values of the products themselves, but also the variation in the measurement values of the measurement system. Thus, the products determined as non-defective articles by the product inspection device may include a product out of the product standard, or the products determined as defective articles may include a product within the product standard. In particular, considering the influence on users of the products, the possibility that the product determined as a non-defective article by the product inspection device is a product out of the product standard needs to be lowered, where the inspection standard, of which condition is stricter than that of the product standard, is usually defined to discriminate the products.
In the product inspection device, the probability that a product out of the product standard is mistakenly determined as a non-defective article based on the inspection standard is called a consumer risk, and the probability that a product within the product standard is mistakenly determined as a defective article based on the inspection standard is called a producer risk. It is generally known that the consumer risk can be reduced by defining the inspection standard having a stricter condition than that of the product standard, but the producer risk becomes rather greater and the percentage (non-defective article rate) of being discriminated as non-defective articles by the product inspection device lowers.
A method of calculating the consumer risk and the producer risk is disclosed in Non-Patent Documents 1 and 2. Non-Patent Document 1 discloses a method of calculating the consumer risk and the producer risk in a product inspection device using the Monte Carlo method. Non-Patent Document 2 discloses a method of calculating the consumer risk and the producer risk assuming that the distributions of the variation in the characteristic values of the products and the variation in the measurement values are normal distributions using a double integral equation.
Non-Patent Document 1: M. Dobbert “Understanding Measurement Risk”, NCSL International Workshop and Symposium, August 2007.
Non-Patent Document 2: David Deaver, “Managing Calibration Confidence in the Real World”, NCSL International Workshop and Symposium, 1995.